Nariko takes a lot of dedication I play with her the most right now and I'm just above average with her in all but 1v1, but if you take the time to learn how to use her she is such a great character.
I would say she is more difficult than to learn then Dante because she is called a combo character, but does she have 1 "real" combo that you can't escape? You gotta have your timing down perfectly just like Dante and hope your openet doesn't know how to defend against her properly.
On the counter there about the same to me.
Nariko's can send back projectiles (with the same properties) and knocks opponents on their butt. Dante's can't reflect anything and launches them into the air.